Nanomaterials in Chemistry

Nanomaterials are particulate materials that are smaller than the wavelength of light. They can be created naturally or engineered.

Nanoparticles are characterized by their surface area and specific reactivity. They can also assemble into larger structures to create new materials.

Examples include the atom-thick carbon allotrope graphene rolled into soccer ball-shaped molecules, known as fullerenes or buckyballs. Other examples are quantum dots, which have been used in composites and solar cells.

Synthesis

In chemistry, nanomaterials refer to materials that exhibit new or enhanced properties due to their small size. Nanomaterials can occur naturally or can be engineered to perform a specific function.

Researchers use various techniques to control the composition, size and surface chemistry of different nanomaterials. These techniques start with molecular precursors and can result in a wide variety of materials with diverse properties.

As a material becomes smaller, more of its atoms are located on the surface, increasing the ratio of surface area to total volume. This makes nanomaterials highly reactive. PNNL has several aberration-corrected scanning transmission electron microscopes and atomic force microscopy capable of providing atomic-level images of nanostructured materials.

One example of a nanomaterial is box-shaped graphene (BSG), which is formed by mechanically cleaving pyrolytic graphite. BSG has unique physical properties, including electrical conductivity and transparency, and can be used in a variety of applications. It also acts as a catalyst in chemical reactions.

Characterization

A chemistry professor at the University of Massachusetts Lowell, Mingdi Yan, describes nanomaterials as “natural, incidental or manufactured materials with particle sizes where 50% or more of the particles have one or more external dimensions in the range 1 nm – 100 nm”.1

Nanomaterials can be classified into two broad categories depending on how many of their dimensions fall within this range. Zero-dimensional (0D) nanomaterials have all of their dimensions in the nanorange and include nanoparticles, nanowires, and nanotubes. One-dimensional (1D) nanomaterials have one dimension outside the nanorange and include nanofilms and monolayers such as graphene.

Compared to macroscopic materials, nanomaterials require unique and sophisticated tools for their characterization. These include a range of analytical techniques that depend on changes in a physical property as the particle size decreases, such as QCM and surface plasmon resonance (SPR). Each tool has its own underlying principles and limits that should be understood. This information is crucial to understanding the interactions of nanomaterials with their environments and biological systems.

Assemblies

Nanoscale materials possess unique physical properties that can improve a wide range of technological applications, including photovoltaics, plasmonics, and magnetic storage. However, precise control over the spatial distribution and orientation of these materials is often requisite to fully realize their potential.

PNNL researchers are developing methods for generating nanomaterial assemblies with specific geometric and compositional arrangements across macroscopic areas and volumes. This is accomplished via a variety of strategies, including manipulation of interparticle physical interactions, modification of nanoparticle surface chemistry, application of external fields, and utilization of physically or chemically patterned templates.

These assembly approaches are important because they can reduce the amount of material needed for a given function. For example, inks made from cyanobacteria and used for dyeing fabrics could use nanometer-scale particles to provide greater color intensity and durability. Additionally, aqueous solutions of protein-based nanoparticles can self-assemble into spheres (called vaults) with hollow cavities that are useful for encapsulating cancer chemotherapeutics or nucleic acids.

Applications

There are a wide variety of applications for nanomaterials, either as fixed (for example attached to a surface or within in a composite) or free. They may be used for catalysis, coatings, sensors, adsorption and drug delivery.

Nanomaterials can be constructed by bottom up techniques, where they are assembled atom by atom or molecule, such as crystal growth for the semiconductor industry and chemical synthesis of large molecules. They can also be constructed through a top down process, such as nanoscale self assembly of polymeric molecules or hierarchical adsorption to a substrate.

The ability to control the size of a nanomaterial opens up new possibilities for use in chemistry. For example, glass fragments with nanoparticles of silver and gold give a unique colour, and a coating with carbon nanotubes improves the strength of yacht masts. A range of traditional techniques can be used to characterize nanomaterials, including transmission electron microscopy and scanning electron microscopy, as well as dynamic light scattering and spectroscopy.

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